Single-phase titration with sodium tetraphenylborate

4 Single-phase titration with sodium tetraphenylborate 

The following method is due to Metcalfe et al. [7]. The authors do not say why they chose to use such an odd concentration of titrant, although it is of no importance. 

Weigh in a 150 ml beaker a sample containing 2-3 millimol of active. 

Dissolve in 40 ml water. If the sample is not very soluble, dissolve it in the minimum of propan-2-ol and then add 40 ml water. Complete dissolution is not essential. 

5 g powdered sucrose and a few drops of 0.2% ethanolic 2,7-dichlorofluorescein and titrate with 0.067 M NaTPB in 0.01 M sodium hydroxide. The solution is initially pink. Near the end-point it becomes deep pink, and at the end-point it changes sharply to yellow. 

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